1. Field of the Invention
This invention relates to a flow sensor, suitable for use within an oil or gas well environment. Specifically, this environment will generally include exposure to high temperatures, high pressures, corrosive media, shock and vibration. Additional requirements are also a small diametrical size, low power consumption and the ability to make measurements while in motion.
2. Description of Related Art
Fluid flow, within an oil or gas well, has long been a very important parameter for well troubleshooting and evaluations. Recent developments have expanded this need to include flow measurements within horizontal sections of a well. This requirement introduces new complications for flow measurement because gas-oil-water flow mixtures will naturally separate within a horizontal pipe. This occurs as the lighter fluid (or gas) rises to the highest elevation while the densest fluid falls to the lowest level. These fluids will also tend to flow at different velocities so that flow measurement at any single point will not give very useful information. Flow measurement, under these conditions then, would be best performed by a multiplicity of small probes to allow profiling of the distribution of the phases.
The most suitable instrument for downhole fluid flow measurement has traditionally been based on a turbine type flow meter. The physical sizes of standard downhole turbine flow meters, however, are not suitable to be utilized for a multi-probe instrument. Small diameter turbine flow meter probes have been designed to profile phase distribution but these are often unreliable because it takes very little to obstruct their freedom to spin.
This is one of two significant limitations for the application of turbine flow meters, in a downhole environment, and both are a consequence of flow measurement based on moving parts. The turbine must spin freely to give an accurate measurement and this can be hampered by many factors such as bearing friction or contaminated fluid media. Bearing friction is generally the primary limiting factor for low flow measurements and bearing wear or fluid contamination generally cause the failure to spin altogether. All of these factors are greatly aggravated by the reduction in diameter which is necessary for multi-probe application within a relatively small diameter pipe. This is unavoidable because the available torque to spin the impeller becomes reduced by both, the moment arm radius of the impeller and its effective area.
It is an object of this invention, then, to provide a fluid flow sensor suitable for making accurate fluid flow measurements within a downhole media and which can also be miniaturized for application in a multi-probe design for phase flow profiling.